If yours is an API 650 tank, annular plates are not required unless:
1) Your tank has a design temperature over 200 DegF and is over 100 feet diameter
2) Your bottom shell course is designed using the allowable stress for materials in Group IV or higher
3) Your tank is in SUG III and located where SDS = 0.5g or greater
4) They are required by the purchaser
Note: this may not be a comprehensive list, but is what I remember from the code.